A person skilled in the art of roller bearing technology will in general be aware that radial roller bearings have an optimum kinematic operating state when sufficiently loaded, at which the roller bodies roll on the raceways of the inner and of the outer bearing ring, without sliding. Furthermore, in the case of radial roller bearings which are operated on low loads at least at times, it is known that the roller body set which comprises the roller bodies and their bearing cage does not rotate at the kinematic rotation speed because of the friction in the bearing or because of the high mass force of the roller body set and the contact force, which is small at times, between the roller bodies and the raceways. In consequence, the rotation speed of the roller body set is less than the kinematic rotation speed, so that the roller bodies are in a kinematically non-optimum state, as a result of which slip occurs between these roller bodies and at least one raceway. In this case, a lubricating film can form on the contact surfaces between the roller bodies and the raceway. However, the lubrication film is destroyed in the event of a sudden change in the rotation speed or load, as a result of which there will no longer be an adequate lubricating film at the contact points where the slip occurs within a very short time. This results in a metallic contact between the raceway and the roller bodies, which slide on the raceway until the roller bodies are accelerated to the kinematic rotation speed. This large speed difference between the raceway and the roller bodies as well as the lack of a separating lubricating film therefore results in high tangential stresses in the surfaces of the raceway and of the roller bodies, which are associated with very severe wear, such as roughening of the raceways, material being torn off and rubbing marks, generally in conjunction with micropitting, thus leading to premature failure of the radial roller bearing.
A radial roller bearing of this generic type has therefore been proposed in FR 2 479 369, which essentially comprises an outer bearing ring with an inner raceway and an inner bearing ring which is arranged coaxially with respect thereto and has an outer raceway, as well as a multiplicity of roller bodies which roll between the bearing rings on their raceways and are held at uniform distances from one another in the circumferential direction by a bearing cage, in which a plurality of roller bodies which are distributed uniformly on the circumference between the roller bodies and the bearing rings, are replaced by hollow rollers in order to avoid the described slip effect and the disadvantages which result from this. These hollow rollers, which additionally are axially somewhat shorter than the other roller bodies, in this case have a slightly larger diameter and a lower modulus of elasticity than the other roller bodies, as a result of which, in the load-free state of the radial roller bearing, they make continuous contact with the bearing rings and therefore ensure a continuous drive of the bearing cage and thus of the other roller bodies at the kinematic rotation speed.
However, in practice, it has been found that the hollow rollers, which are subject Lo continuous bending fatigue load as a result of their permanent deformation, in radial roller bearings such as these represent potential weak points of the roller bearing in terms of their load capability and fatigue strength, thus resulting in reduced load-carrying capability and a shorter life of the roller bearing. For example, it has been found that local stress peaks occur, in particular, on the inner envelope surfaces of the hollow rollers, leading to cracking and finally to fracture of the hollow rollers during long-term operation of the roller bearing. This was due in particular to the use of standard roller-bearing steel for the hollow rollers and their standard heat treatment, in which the hollow rollers were provided with a continuously martensitic structure by hardening at a temperature of 860° C., quenching in an oil or salt bath and tempering at 190±10° C., a very high level of hardness of which structure admittedly ensures that the hollow rollers have high rolling-over strength, although the low ductility and the lack of inherent compression stresses are unsuitable, in particular for the continuous bending fatigue loads on their inner envelope surfaces. One obvious measure to avoid such stress concentrations would admittedly be to increase the dimensions of both the hollow rollers and the other roller bodies, but this would necessarily result in an increase in the total space required for the bearing and an increase in the production costs for the roller bearing.